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Bioimpedance spectroscopy is used in a wide range of biomedical applications. This paper presents an integrated analog readout, which employs synchronous detection to perform galvanostatic multi-channel, multi-frequency bioimpedance measurements. The circuit was fabricated in a 0.35-µm CMOS technology and occupies an area of 1.52 mm 2 . The effect of random dc offsets is investigated, along with the use of chopping to minimize them. Impedance measurements of a known RC load and skin (using commercially available electrodes) demonstrate the operation of the system over a frequency range up to 1 MHz. The circuit operates from a ±2.5 V power supply and has a power consumption of 3.4-mW per channel.

. A simulation study of the combined thermoelectric extracellular stimulation of the sciatic nerve of the Xenopus laevis: the localized transient heat block. IEEE Transactions on Biomedical Engineering, 59(6), pp. 1758 -1769 . doi: 10.1109 /TBME.2012 This is the accepted version of the paper.This version of the publication may differ from the final published version. 1  Abstract-This paper presents the response of the Xenopus laevis nerve fibers to combinations of electrical (cuff electrodes) and optical (infrared laser, low power sub-5mW) stimulation. Assuming that the main effect of the laser irradiation on the nerve tissue is the localized temperature increase, this paper analyzes and gives new insights into the function of the combined thermoelectric stimulation on both excitation and blocking of the nerve action potentials (AP). The calculations involve a finite-element model (COMSOL) to represent the electrical properties of the nerve and cuff. Electric field distribution along the nerve was computed for the given stimulation current profile and imported into a NEURON model, which was built to simulate the electrical behavior of myelinated nerve fiber under extracellular stimulation. The main result of this study of combined thermoelectric stimulation showed that local temperature increase, for the given electric field, can create a transient block of both the generation and propagation of the APs. Some preliminary experimental data in support of this conclusion are also shown. Permanent

Current drivers are fundamental circuits in bioimpedance measurements including electrical impedance tomography (EIT). In the case of EIT, the current driver is required to have a large output impedance to guarantee high current accuracy over a wide range of load impedance values. This paper presents an integrated current driver which meets these requirements and is capable of delivering large sinusoidal currents to the load. The current driver employs a differential architecture and negative feedback, the latter allowing the output current to be accurately set by the ratio of the input voltage to a resistor value. The circuit was fabricated in a 0.6- μm high-voltage CMOS process technology and its core occupies a silicon area of 0.64 mm (2) . It operates from a ± 9 V power supply and can deliver output currents up to 5 mA p-p. The accuracy of the maximum output current is within 0.41% up to 500 kHz, reducing to 0.47% at 1 MHz with a total harmonic distortion of 0.69%. The output impedance is 665 k Ω at 100 kHz and 372 k Ω at 500 kHz.